代码实现续
核心执行引擎 Executor 的实现
/**
* 执行器的实现
*
* @name: SimpleExecutor
* @author: terwer
* @date: 2022-03-14 16:53
**/
public class SimpleExecutor implements Executor {
@Override
public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {
// 注册驱动,获取链接
Connection connection = configuration.getDataSource().getConnection();
// 获取sql语句
// 获取的sql
// select * from user where id = #{id} and username = #{username}
// 转换后的sql
// select * from user where id = ? and username = ?
String sql = mappedStatement.getSql();
// 转换sql语句
BoundSql boundSql = getBoundSql(sql);
// 获取预处理对象
PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());
// 设置参数
// 参数全路径
String parameterType = mappedStatement.getParameterType();
Class<?> parameterClass = getClassType(parameterType);
List<ParameterMapping> parameterMappingList = boundSql.getParameterMappingList();
for (int i = 0; i < parameterMappingList.size(); i++) {
ParameterMapping parameterMapping = parameterMappingList.get(i);
String content = parameterMapping.getContent();
Field field = parameterClass.getDeclaredField(content);
field.setAccessible(true);
Object value = field.get(params[0]);
preparedStatement.setObject(i + 1, value);
}
// 执行sql
ResultSet resultSet = preparedStatement.executeQuery();
String returnType = mappedStatement.getResultType();
Class<?> resultTypeClass = getClassType(returnType);
Object o = resultTypeClass.newInstance();
ArrayList<Object> objects = new ArrayList<>();
// 封装返回结果集
while (resultSet.next()) {
ResultSetMetaData metaData = resultSet.getMetaData();
for (int i = 1; i <= metaData.getColumnCount(); i++) {
String columnName = metaData.getColumnName(i);
// 获取字段值
Object value = resultSet.getObject(columnName);
// 使用反射或者内省,根据数据库表和实体的对应关系完成封装
PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);
Method writeMethod = propertyDescriptor.getWriteMethod();
writeMethod.invoke(o, value);
}
objects.add(o);
}
return (List<E>) objects;
}
private Class<?> getClassType(String parameterType) throws ClassNotFoundException {
if (parameterType != null) {
Class<?> aClass = Class.forName(parameterType);
return aClass;
}
return null;
}
/**
* 1、将#{}使用?代替
* 2、解析出#{}的值进行存储
*
* @param sql
* @return
*/
private BoundSql getBoundSql(String sql) {
// 标记处理类,配合标记解析器完成对占位符的解析
ParameterMappingTokenHandler tokenHandler = new ParameterMappingTokenHandler();
GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", tokenHandler);
// 解析后的sql
String parseSql = genericTokenParser.parse(sql);
// 解析的参数名称
List<ParameterMapping> parameterMappings = tokenHandler.getParameterMappings();
BoundSql boundSql = new BoundSql(parseSql, parameterMappings);
return boundSql;
}
}
运行效果
问题修复
1、selectList 打印的全部是同一个值
/Library/Java/JavaVirtualMachines/jdk1.8.0_291.jdk/Contents/Home/bin/java -... com.intellij.rt.junit.JUnitStarter -ideVersion5 -junit4 com.terwergreen.test.IPersistenceTest,test2
Connected to the target VM, address: '127.0.0.1:50317', transport: 'socket'
log4j:WARN No appenders could be found for logger (com.mchange.v2.log.MLog).
log4j:WARN Please initialize the log4j system properly.
User{id=5, username='dali'}
User{id=5, username='dali'}
User{id=5, username='dali'}
User{id=5, username='dali'}
Disconnected from the target VM, address: '127.0.0.1:50317', transport: 'socket'
Process finished with exit code 0
修正方案
修正后
/Library/Java/JavaVirtualMachines/jdk1.8.0_291.jdk/Contents/Home/bin/java -... com.intellij.rt.junit.JUnitStarter -ideVersion5 -junit4 com.terwergreen.test.IPersistenceTest,test2
Connected to the target VM, address: '127.0.0.1:50820', transport: 'socket'
log4j:WARN No appenders could be found for logger (com.mchange.v2.log.MLog).
log4j:WARN Please initialize the log4j system properly.
User{id=1, username='tyw'}
User{id=2, username='张月'}
User{id=4, username='haha'}
User{id=5, username='dali'}
Disconnected from the target VM, address: '127.0.0.1:50820', transport: 'socket'
Process finished with exit code 0
代码仓库
文章更新历史
2024/04/24 同步文章到其他平台
2022/05/08 初稿
本文实现了一个简单的MyBatis框架,包括数据库连接、SQL语句解析、参数设置、结果封装等功能。具体实现包括配置文件加载、Mapper接口与SQL语句映射、动态SQL处理、连接池管理等。通过这个框架可以简化数据库操作,提高开发效率。
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